Mojo C++ bindings: support mapping mojo string to WTF::String.

mojo/mojo_edk_tests.gyp

Index: mojo/mojo_edk_tests.gyp
diff --git a/mojo/mojo_edk_tests.gyp b/mojo/mojo_edk_tests.gyp
index 03e60d3862ef730e1742806b482bac48bad21d21..80e5cb8a0d7300e49ddb8c70f9208ae2cd92c858 100644
--- a/mojo/mojo_edk_tests.gyp
+++ b/mojo/mojo_edk_tests.gyp
@@ -47,6 +47,7 @@
       'type': 'executable',
       'dependencies': [
         '../testing/gtest.gyp:gtest',
+        '../third_party/WebKit/Source/wtf/wtf_tests.gyp:wtf_unittest_helpers',
         'mojo_base.gyp:mojo_environment_chromium',
         'mojo_edk.gyp:mojo_run_all_unittests',
         'mojo_public.gyp:mojo_cpp_bindings',
@@ -58,6 +59,8 @@
         'mojo_public.gyp:mojo_public_test_interfaces_chromium',
         'mojo_public.gyp:mojo_public_test_interfaces_struct_traits',
         'mojo_public.gyp:mojo_public_test_utils',
+        'mojo_public.gyp:mojo_public_test_wtf_types',
+        'mojo_public.gyp:mojo_public_test_wtf_types_wtf',
         'mojo_public.gyp:mojo_utility',
       ],
       'sources': [
@@ -101,6 +104,7 @@
         'public/cpp/bindings/tests/type_conversion_unittest.cc',
         'public/cpp/bindings/tests/union_unittest.cc',
         'public/cpp/bindings/tests/validation_unittest.cc',
+        'public/cpp/bindings/tests/wtf_types_unittest.cc',
       ],
     },
     {